Multistage multipactor



50 manner of thin film of thorium, caesium, potas- Patented Dec. 27, 1938 2,141,837

UNITED STATES PATENT OFFICE MULTISTAGE MULTIPACTOR Philo T. Farnsworth, San Francisco, Calif., as-

signor to Farnsworth Televisionlncorporated, San Francisco, Calif., a corporation of California Application June 1, 1936, Serial No. 82,888

3 Claims. (01. 250-175) My invention relates to electron multipliers, surface being necessary for this disk. It will be and more particularly to that type wherein elecnoted that the disks are of progressively introns are directed to successively impact a series creased diameter and arranged Op the ends of surfaces to produce a current augmented by of the cylinders.

5 secondary emission at each impact. The multiplier is rendered active by activating 5 Among the objects of my invention are: To the filament 9 from a source 25 and attaching a provide an electron multiplier embodying simresistor 26 across a source of potential 21, taps plicity in construction; to provide an electron 28 to 33 being taken from the resistor and leadmultiplier in which space charge limitations are ing to the filament and alternately to the cylin- 0 a minimum; and to provide an electron multiders and plates H, l1, l2, l9, and II, respectively, plier the arrangement of which is such as to to produce progressively increasing potentials facilitate the movement of electrons. thereon, the end of the resistor being connected Other objects of my invention will be apparent through output impedance 35 to the anode plate or will be specifically pointed out in the descrip- 24, the impe arranged f utilization tion forming a part of this specification, but I do in any well known manner. 1

not limit myself to the embodiment of the in- Energized in the manner above indicated, elecvention herein described, as various forms may trons leaving he filament 9 are accelerated be adopted within the scope of the claims. through the grid l0, and attracted to the sur- In the drawing: face Ila of higher potential, impact the same to Figure 1 is a sectional view through apreferred cause secondary electrons to be emitted. The 20 embodiment of my electron multiplier. secondary electrons so emitted are attracted to Figure 2 is a sectional view taken in the line the disk surface Ha ina similar manner with 2-2 of Figure 1. secondary emission resulting at surface l'la.

In the preferred embodiment of my invention, Surface I'la acting as a source, the electrons an evacuated cylindrical envelope I closed by emitted are attracted to surface l2a. 25 end walls 2 and 4 has supported axially there- In this manner the fiow of electrons between within, as by leads 5 and B sealed through stem successive surfaces is augmented and the elecl, a filamentary cathode 9 and a grid I0. A trons emitted from surface Ma are collected on series of short cylinders II, I 2 and M are supthe anode 24. Itwill be observed that the sucported in spaced co-axial relation longitudinally cessive emitting surfaces are so relatively ar- 30 of the envelope axis by means of anchor, pins l5 ranged that the electrons take a zig-zag course, and leads l6 respectively fused in and sealed cascading from surface to surface in the manner through the envelope l. The endmost cylinder indicated generally by the arrows in Figure 1,

l l of the series is disposed adjacent the cathode and thatthe path continues to increase in cross- 35 9 and the cylinders of the series are of progressectional area as the multiplication increases,

sively increasing diameters as shown. The inthus holding electron concentrations within deterior surface elements Ila, [2a, and Ma of these sirable limits. j cylinders are treated to provide a surface capable While I have shown the first emitting surface of readily emitting secondary electrons at a ratio to be cylindrical, it is apparent that the electrons 40 greater t an unity wh n pa d y a p ma y from the cathode may be first impacted upon the Clectron traveling at h Proper Velocitydisk surface l'la, the surrounding cylinder H be- Dispcsed within the cylinders l2 a in ing omitted. It is furthermore apparent that any spaced relation thereto are disks l1 and I9 supdesired number of multiplications may be ported by leads and i f f Stlem tained by varying the number of surfaces, and

a zzof the envelipe i 8 surfaces that either a disk or a cylinder may be utilized and 19a are likewise sensitized for secondary for an anode collector emission and I have found that the surface ele- I f l tro um ments Ha, l2a, Ma, Fla, and l9a may be sensiz g gg iz gzggg gg g 23 2;; a tlzed by the deposltlon thereon m any wen known ing out the objects of the present invention, it is sium, or calcium. However, any material'capaunderstood that varioujs modificatifms and ble of emitting secondaries on impact is satis- Changes may be made Wlthout departmg from factory the invention which is considered to include all A final disk 24 similar in structure to disks I! such modifications as lie within the scope of the and I9 is provided as a collector, no sensitized following claims:

said cylinders and within the succeeding cylinder.

3. An electron multiplier comprising an envelope containing a source of electrons, a cylindrical surface capable of producing secondary 5 electrons at a ratio greater than unity upon electron impact therewith surrounding said source to receive electrons from said source, a planar surface opposite one end of said cylindrical surface and collecting means surrounding said 10 planar surface to attract secondary electrons.

PHILO T. FARNSWORTH. 

